Method for performing path reselection in wireless communication system and apparatus therefor

ABSTRACT

The present specification provides a method for performing a radio link failure (RLF) recovery procedure in a wireless communication system.The method performed by a first user equipment (UE) includes, wherein the first UE is connected to a base station via a UE-to-UMTS (Uu) link and is connected to a second UE via a sidelink, determining a path for performing the RLF recovery procedure when a RLF is detected on the Uu link, and performing an RRC connection re-establishment procedure in order to recover the RLF through the determined path.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/499,711, filed Sep. 30, 2019, which is a National Stage applicationunder 35 U.S.C. § 371 of International Application No.PCT/KR2018/003596, filed on Mar. 27, 2018, which claims the benefit ofU.S. Provisional Application No. 62/479,185, filed on Mar. 30, 2017. Thedisclosures of the prior applications are incorporated by reference intheir entirety.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly to a method for performing a path reselection and adevice supporting the same.

BACKGROUND ART

A mobile communication system has been developed to provide a voiceservice while ensuring an activity of a user. However, in the mobilecommunication system, not only a voice but also a data service isextended. At present, due to an explosive increase in traffic, there isa shortage of resources and users demand a higher speed service, and asa result, a more developed mobile communication system is required.

Requirements of a next-generation mobile communication system should beable to support acceptance of explosive data traffic, a dramaticincrease in per-user data rate, acceptance of a significant increase inthe number of connected devices, very low end-to-end latency, andhigh-energy efficiency. To this end, various technologies areresearched, which include dual connectivity, massive multiple inputmultiple output (MIMO), in-band full duplex, non-orthogonal multipleaccess (NOMA), super wideband support, device networking, and the like.

SUMMARY

An object of the present specification is to provide a method forreselecting a path performing a radio link failure (RLF) recoveryprocedure when a RLF occurs on a UE-to-UMTS (Uu) link.

Another object of the present specification is to provide a method forreselecting a relaying path based on whether to support a service type,a congestion level of a hop, or the like.

Technical problems to be solved by the present invention are not limitedby the technical problems mentioned above, and other technical problemswhich are not mentioned above can be clearly understood from thefollowing description by those skilled in the art to which the presentinvention pertains.

The present specification provides a method for performing, by a firstuser equipment (UE), a radio link failure (RLF) recovery procedure in awireless communication system, the method comprising, wherein the firstUE is connected to a base station via a UE-to-UMTS (Uu) link and isconnected to a second UE via a sidelink, determining a path forperforming the RLF recovery procedure when a RLF is detected on the Uulink; and performing an RRC connection re-establishment procedure inorder to recover the RLF through the determined path, wherein the pathfor performing the RLF recovery procedure is determined based on afactor related to data characteristic of the first UE, wherein thedetermined path is the Uu link or the sidelink.

In the present specification, the factor related to the datacharacteristic of the first UE is a Qos class identifier (QCI), a packetdelay budget, or a priority.

In the present specification, the method further comprises receiving,from the base station, a threshold for the factor related to the datacharacteristic of the first UE, wherein the path for performing the RLFrecovery procedure is determined through a comparison between the factorrelated to the data characteristic of the first UE and the receivedthreshold.

In the present specification, when the determined path is the sidelink,the RRC connection re-establishment procedure further comprises sending,to the second UE, a request message for requesting a RRC connectionre-establishment; and receiving, from the second UE, a response messageto the request message.

In the present specification, the first UE is a remote UE, and thesecond UE is a relay UE.

The present specification provides a method for reselecting, by a firstnode, a relaying path in a wireless communication system, the methodcomprising, wherein the first node is connected to a second node via aUE-to-UMTS (Uu) link, transmitting and receiving data with one or morenodes via the Uu link; reselecting the relaying path when a radio linkfailure (RLF) is detected on the Uu link or a specific condition is met;and transmitting and receiving data with at least one node through thereselected relaying path, wherein the specific condition is whether tosupport a 5G Qos indicator (5QI) level on a node, whether to support aspecific service type on the node, a congestion level of a hop, or abeam state.

In the present specification, the method further comprises, when therelaying path is reselected using a distributed manner, exchangingassistance information with the at least one node.

In the present specification, the assistance information is exchangedperiodically or in an event triggered manner.

In the present specification, when the RLF is not detected on the Uulink, the relaying path is reselected depending on the specificcondition.

In the present specification, the specific service type is enhancedmultimedia broadband (eMBB), ultra reliable low latency communication(URLLC), or massive IoT (MIoT).

In the present specification, the first node is a relay node, and thesecond node is a donor node. The second node is connected to a 5thgeneration core network.

The present specification provides a first user equipment (UE) forperforming a radio link failure (RLF) recovery procedure in a wirelesscommunication system, the first UE comprising a radio frequency (RF)module configured to transmit and receive a radio signal; and aprocessor functionally connected to the RF module, wherein the first UEis connected to a base station via a UE-to-UMTS (Uu) link and isconnected to a second UE via a sidelink, wherein the processor isconfigured to determine a path for performing the RLF recovery procedurewhen a RLF is detected on the Uu link; and perform an RRC connectionre-establishment procedure in order to recover the RLF through thedetermined path, wherein the path for performing the RLF recoveryprocedure is determined based on a factor related to data characteristicof the first UE, wherein the determined path is the Uu link or thesidelink.

The present specification has an effect capable of implementingtransmission and reception of data suitable for 5G requirements byapplying parameters related to a service flow considered in a nextgeneration communication system such as 5G as well as RSRP to therebyreselect a path.

Effects obtainable from the present invention are not limited by theeffects mentioned above, and other effects which are not mentioned abovecan be clearly understood from the following description by thoseskilled in the art to which the present invention pertains.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the present invention and constitute a part of thedetailed description, illustrate embodiments of the present inventionand together with the description serve to explain the principle of thepresent invention.

FIG. 1 illustrates an example of a network structure of an evolveduniversal terrestrial radio access network (E-UTRAN) to which thepresent invention is applicable.

FIG. 2 illustrates structures of an E-UTRAN and an EPC in a wirelesscommunication system to which the present invention is applicable.

FIG. 3 illustrates a radio interface protocol structure between a UE andan E-UTRAN in a wireless communication system to which the presentinvention is applicable.

FIG. 4 schematically illustrates a structure of a physical channel in awireless communication system to which the present invention isapplicable.

FIG. 5 illustrates a contention based random access procedure in awireless communication system to which the present invention isapplicable.

FIG. 6 illustrates an example of a procedure of transmitting andreceiving sidelink UE information.

FIG. 7 illustrates an example of a method of informing a base station ofa sidelink RAT type proposed by the present specification.

FIG. 8 illustrates an example of a path reselection procedure when a RLFoccurs in a NB-IoT network proposed by the present specification.

FIG. 9 is a flow chart illustrating an example of a path reselectionscheme by a UE proposed by the present specification.

FIG. 10 illustrates an example of an IAB topology structure.

FIG. 11 illustrates an example of in-band and out-band IABs.

FIG. 12 illustrates an example of a situation where a path reselectionis necessary in an NR network.

FIG. 13 illustrates an example of an NR network proposed by the presentspecification.

FIG. 14 is a flow chart illustrating another example of a pathreselection scheme by a UE proposed by the present specification.

FIG. 15 illustrates a block configuration diagram of a wirelesscommunication device to which methods proposed by the presentspecification are applicable.

FIG. 16 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

FIG. 17 illustrates an example of a RF module of a wirelesscommunication device to which a method proposed by the presentspecification is applicable.

FIG. 18 illustrates another example of a RF module of a wirelesscommunication device to which a method proposed by the presentspecification is applicable.

SUMMARY

In what follows, preferred embodiments according to the presentinvention will be described in detail with reference to appendeddrawings. The detailed descriptions given below with reference toappended drawings are intended only to provide illustrative embodimentsof the present invention and do not represent the only embodimentsthereof. The detailed descriptions of the present invention belowinclude specific details for the purpose of comprehensive understandingof the present invention. However, those skilled in the art may readilyunderstand that the present invention can be implemented without thosespecific details.

For some case, in order to avoid inadvertently making the technicalconcept of the present invention obscured, the structure and theapparatus well-known to the public can be omitted or illustrated in theform of a block diagram with respect to essential functions of thestructure and the apparatus.

A base station in this document is defined as a terminal node of anetwork which carries out communication directly with a terminal.Particular operations in this document described to be carried out by abase station may be carried out by an upper node of the base stationdepending on the situation. In other words, it is evident that in anetwork consisting of a plurality of network nodes including a basestation, various operations carried out for communication with terminalscan be carried out the base station or other network nodes other thanthe base station. The term of base station (BS) can be substituted forby those terms such as fixed station, Node B, evolved-NodeB (eNB), basetransceiver system (BTS), and access point (AP). Also, a terminal may bestationary or mobile and can be referred to by different terms such as aUser Equipment (UE), Mobile Station (MS), User Terminal (UT), MobileSubscriber Station (MSS), Subscriber Station (SS), Advanced MobileStation (AMS), Wireless Terminal (WT), Machine-Type Communication (MTC)device, Machine-to-Machine (M2M) device, and Device-to-Device (D2D)device.

In what follows, downlink transmission denotes communication from the BSto the UE, and uplink transmission denotes communication from the UE tothe BS. In the downlink transmission, a transmitter can be a part of theBS while a receiver can be a part of the UE. In the uplink transmission,a transmitter can be a part of the UE while a receiver can be a part ofthe base station.

Particular terms used in the descriptions below are introduced to helpunderstand the present invention and can be modified in various otherways as long as a modified use thereof does not depart from thetechnical principles and concept of the present invention.

Technologies described below can be used by various wireless accesssystems based on the scheme such as CDMA (code division multipleaccess), FDMA (frequency division multiple access), TDMA (time divisionmultiple access), OFDMA (orthogonal frequency division multiple access),SC-FDMA (single carrier frequency division multiple access), and NOMA(non-orthogonal multiple access). The CDMA scheme can be implemented bya radio technology such as universal terrestrial radio access (UTRA) andCDMA2000. The TDMA scheme can be implemented by a radio technology suchas global system for mobile communications (GSM), general packet radioservice (GPRS), and enhanced data rates for GSM evolution (EDGE). TheOFDMA scheme can be implemented by such as radio technology as definedby the IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, andevolved UTRA (E-UTRA). The UTRA is a part of standards specifying theuniversal mobile telecommunications system (UMTS). The 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part ofstandards of the evolved UMTS (E-UMTS) employing the E-UTRA, employingthe OFDMA scheme for downlink transmission and the SC-FDMA scheme foruplink transmission. The LTE-A (Advanced) is an enhancement of the 3GPPLTE standard.

The embodiments of this document can be supported by at least one of thestandard specifications for wireless access systems such as the IEEE802, 3GPP, and 3GPP2. In other words, the standard specifications can beused to support those steps or parts among the embodiments of thepresent invention not explicitly described in favor of clarifying thetechnical principles thereof. Also, for technical definitions of theterms used in this document, the standard documents should be consulted.

For the purpose of clarity, this document is described based on the 3GPPLTE/LTE-A standard; however, it should be understood that the presentinvention is not limited to the specific standard.

FIG. 1 illustrates an example of a network structure of an evolveduniversal terrestrial radio access network (E-UTRAN) to which thepresent invention is applicable.

An E-UTRAN system is an evolved version of the existing UTRAN system andmay be, for example, 3GPP LTE/LTE-A system. Communication networks arewidely deployed to provide various communication services such as voice(e.g., voice over Internet protocol (VoIP)) through IMS and packet data.

Referring to FIG. 1 , an E-UMTS network includes an E-UTRAN, an EPC, andone or more UEs. The E-UTRAN consists of eNBs that provide control planeand user plane protocol to the UE, and the eNBs are interconnected witheach other by means of the X2 interface.

X2 user plane (X2-U) interface is defined between the eNBs. The X2-Uinterface provides non-guaranteed delivery of a user plane packet dataunit (PDU). X2 control plane (X2-CP) interface is defined between twoneighboring eNBs. The X2-CP performs functions of context deliverybetween the eNBs, control of user plane tunnel between a source eNB anda target eNB, delivery of handover-related messages, uplink loadmanagement, and the like.

The eNB is connected to the UE via a radio interface and is connected toevolved packet core (EPC) by means of the S1 interface.

S1 user plane (S1-U) interface is defined between the eNB and a servinggateway (S-GW). S1 control plane interface (S1-MME) is defined betweenthe eNB and a mobility management entity (MME). The S1 interfaceperforms functions of evolved packet system (EPS) bearer servicemanagement, non-access stratum (NAS) signaling transport, networksharing, MME load balancing management, and so on. The S1 interfacesupports many-to-many-relation between the eNB and the MME/S-GW.

The MME may perform various functions such as NAS signaling security,access stratum (AS) security control, inter-core network (CN) nodesignaling for supporting mobility between 3GPP access networks, idlemode UE reachability (including control and execution of pagingretransmission), tracking area identity (TAI) management (for UE in idleand active modes), PDN GW and SGW selection, MME selection for handoverwith MME change, SGSN selection for handover to 2G or 3G 3GPP accessnetworks, roaming, authentication, bearer management functions includingdedicated bearer establishment, support of public warning system (PWS)(including earthquake and tsunami warning system (ETWS) and commercialmobile alert system (CMAS)) message transmission, and the like.

FIG. 2 illustrates structures of an E-UTRAN and an EPC in a wirelesscommunication system to which the present invention is applicable.

Referring to FIG. 2 , an eNB may perform functions of selection ofgateway (e.g., MME), routing to gateway during radio resource control(RRC) activation, scheduling and transmission of broadcast channel(BCH), dynamic resource allocation to the UE in uplink and downlink, andmobility control connection in LTE_ACTIVE state. As described above, thegateway in the EPC may perform functions of paging origination, LTE_IDLEstate management, ciphering of user plane, bearer control of systemarchitecture evolution (SAE), and ciphering and integrity protection ofNAS signaling.

FIG. 3 illustrates a radio interface protocol structure defined betweena UE and an E-UTRAN in a wireless communication system to which thepresent invention can be applied.

FIG. 3(a) illustrates a radio protocol structure of a control plane, andFIG. 3(b) illustrates a radio protocol structure of a user plane.

With reference to FIG. 3 , layers of a radio interface protocol betweenthe UE and the E-UTRAN can be classified into a first layer (L1), asecond layer (L2), and a third layer (L3) based on the lower threelayers of the open system interconnection (OSI) model that is well-knownin the communication system technology field. The radio interfaceprotocol between the UE and the E-UTRAN is divided horizontally into aphysical layer, a data link layer, and a network layer; and dividedvertically into a user plane which is a protocol stack for datainformation transmission and a control plane which is a protocol stackfor transmission of a control signal.

The control plane refers to a path along which control messages for theUE and the network to manage calls are transmitted. The user planerefers to a path along which data created in the application layer, forexample, voice data or Internet packet data are transmitted. In whatfollows, the control plane and the user plane of the radio protocol willbe described.

The physical (PHY) layer belonging to the first layer provides aninformation transfer service to an upper layer by using a physicalchannel. The PHY layer is connected to the medium access control (MAC)layer belonging to the upper layer through a transport channel, and dataare transferred between the MAC layer and the PHY layer through thetransport channel. The transport channel is classified according to howand with what characteristics data are transferred through a radiointerface. And a physical channel is employed to transfer data betweendisparate physical layers and between a physical layer of a transmitterend and a physical layer of a receiver end. The physical layer ismodulated by OFDM scheme and uses time and frequency as radio resources.

There are a few physical control channels used in the physical layer. Aphysical downlink control channel (PDCCCH) informs the UE of a pagingchannel (PCH), resource allocation of a downlink shard channel (DL-SCH),and hybrid automatic repeat request (HARQ) information related to anuplink shared channel (UL-SCH). Also, the PDCCH can carry an uplinkgrant which informs the UE of resource allocation for uplinktransmission. A physical control format indicator channel (PDFICH)informs the UE of the number of OFDM symbols used for the PDCCHs and istransmitted for each subframe. A physical HARQ indicator channel (PHICH)carries a HARQ acknowledge (ACK)/non-acknowledge (NACK) signal inresponse to the uplink transmission. A physical uplink control channel(PUCCH) carries requests scheduling of the HARQ ACK/NACK signal fordownlink transmission and carries uplink control information such as achannel quality indicator (CQI). A physical uplink shared channel(PUSCH) carries an UL-SCH.

The MAC layer of the second layer (L2) provides a service to its upperlayer, radio link control (RLC) layer, through a logical channel.Functions of the MAC layer includes mapping between a logical channeland a transport channel; and multiplexing/demultiplexing of transportblocks provided to a physical channel on a transport channel of a MACservice data unit (SDU) belonging to the logical channel.

The RLC layer of the second layer (L2) supports reliable transmission ofdata. Functions of the RLC layer include concatenation, segmentation,and reassembly of the RLC SDU. To ensure various levels of quality ofservice (QoS) that a radio bearer (RB) requests, the RLC layer providesthree operating modes: transparent mode (TM), unacknowledged mode (UM),and acknowledge mode (AM). The AM RLC provides error correction throughan automatic repeat request (ARQ). Meanwhile, in case the MAC layercarries the RLC function, the RLC layer can be included as a functionalblock of the MAC layer.

A packet data convergence protocol (PDCP) layer of the second layer (L2)carries functions of transfer of user data in the user plane, headercompression, and ciphering. The header compression refers to thefunction of reducing the size of the IP packet header which carriesrelatively large and unnecessary control information so that Internetprotocol (IP) packets such as the Internet protocol version 4 (IPv4) orthe Internet protocol version 6 (IPv6) can be transmitted efficientlythrough a radio interface with narrow bandwidth. Functions of the PDCPlayer in the control plane include transfer of plane data andciphering/integrity protection.

The radio resource control (RRC) layer located in the lowest part of thethird layer (L3) is defined only in the control plane. The RRC layercontrols radio resources between the UE and a network. To this end, theUE and the network exchanges RRC messages through the RRC layer. The RRClayer controls a logical channel, a transport channel, and a physicalchannel related to configuration, re-configuration, and release of radiobearers. A radio bearer refers to a logical path that the second layer(L2) provides for data transmission between the UE and the network.Configuring a radio bearer indicates that a radio protocol layer andchannel characteristics are defined for providing a particular serviceand specific parameters and an operating method thereof are set up. Aradio bearer is again divided into a signaling RB (SRB) and a data RB(DRB). The SRB is used as a path for transmitting RRC messages in thecontrol plan, and the DRB is used as a path for transmitting user datain the user plane.

The non-access stratum (NAS) layer located in the upper hierarchy of theRRC layer performs the function of session management, mobilitymanagement, and so on.

A cell constituting an eNB has bandwidth chosen from among 1.25, 2.5, 5,10, 2 MHz and provides a downlink or an uplink transmission service toUEs. Bandwidth configuration can be carried out so that different cellshave bandwidth different from each other.

Downlink transport channels for transporting data from a network to a UEinclude a broadcast channel (BCH) which transmits system information, aPCH which transmits a paging message, a DL-SCH which transmits usertraffic or a control message. Downlink multicast or broadcast servicetraffic or a control message may be transmitted through the DL-SCH orthrough a separate multicast channel (MCH). Meanwhile, uplink transportchannels for transporting data from the UE to the network include arandom access channel (RACH) which transmits the initial control messageand an uplink shared channel which transmits user traffic or a controlmessage.

A logical channel lies in the upper hierarchy of a transport channel andis mapped to the transport channel. A logical channel is divided into acontrol channel for transmission of control area information and atraffic channel for transmission of user area information. Logicalchannels include a broadcast control channel (BCCH), a paging controlchannel (PCCH), a common control channel (CCCH), a dedicated controlchannel (DCCH), a multicast control channel (MCCH), a dedicated trafficchannel (DTCH), and a multicast traffic channel (MTCH). The PCCH is adownlink channel transferring paging information and is used when thenetwork does not know a cell to which the UE belongs. The CCCH is usedby a UE having no RRC connection with the network. The MCCH is apoint-to-multipoint downlink channel which is used to transfermultimedia broadcast and multicast service (MBMS) control informationfrom the network to the UE. The DCCH is a point-to-point bi-directionalchannel that is used by a UE having RRC connection transferringdedicated control information between the UE and the network. The DTCHis a point-to-point channel which is dedicated to one UE fortransferring user information that can exist in uplink and downlink. TheMTCH is a point-to-multipoint downlink channel for transmitting trafficdata from the network to the UE.

In case of uplink connection between the logical channel and thetransport channel, the DCCH may be mapped to UL-SCH, the DTCH may bemapped to UL-SCH, and the CCCH may be mapped to UL-SCH. In case ofdownlink connection between the logical channel and the transportchannel, the BCCH may be mapped to BCH or DL-SCH, the PCCH may be mappedto PCH, the DCCH may be mapped to DL-SCH, the DTCH may be mapped toDL-SCH, the MCCH may be mapped to MCH, and the MTCH may be mapped toMCH.

FIG. 4 schematically illustrates a structure of a physical channel in awireless communication system to which the present invention isapplicable.

Referring to FIG. 4 , the physical channel transfers signaling and dataon radio resources consisting of one or more subcarriers in a frequencydomain and one or more symbols in a time domain.

One subframe with 1.0 ms length consists of a plurality of symbols.Specific symbol(s) of the subframe (e.g., a first symbol of thesubframe) may be used for PDCCH. The PDCCH carries information aboutdynamically allocated resources (e.g., resource block, modulation andcoding scheme (MCS), etc.).

Random Access Procedure

A random access procedure provided by the LTE/LTE-A system is describedbelow.

The random access procedure is performed when a UE performs initialaccess in an RRC idle state because it does not have RRC connection withan eNB, when the UE performs an RRC connection re-establishmentprocedure, and the like.

The LTE/LTE-A system provides both a contention based random accessprocedure in which the UE randomly selects to use one preamble in aspecific set, and a non-contention based random access procedure inwhich the eNB uses a random access preamble that the eNB allocates toonly a specific UE, in a process of selecting a random access preamble(RACH preamble).

FIG. 5 illustrates a contention based random access procedure in awireless communication system to which the present invention isapplicable.

(1) First Message (Msg 1, Message 1)

First, a UE randomly selects one random access preamble (RACH preamble)from a set of random access preambles indicated through systeminformation or a handover command, selects a physical RACH (PRACH)resource capable of transmitting the random access preamble, andtransmits the selected PRACH.

An eNB receiving the random access preamble from the UE decodes therandom access preamble and obtains an RA-RNTI. The RA-RNTI related tothe PRACH, to which the random access preamble is transmitted, isdetermined by time-frequency resources of the random access preambletransmitted by the corresponding UE.

(2) Second Message (Msg 2, Message 2)

The eNB transmits, to the UE, a random access response addressed to theRA-RNTI obtained via the preamble on the first message. The randomaccess response may include a random access (RA) preambleindex/identifier, an uplink (UL) grant informing of uplink radioresources, a temporary cell-RNTI (TC-RNTI), and time alignment commands(TACs). The TAC is information indicating a time alignment command thatthe eNB sends to the UE in order to maintain an uplink time alignment.The UE updates an uplink transmission timing using the TAC. When the UEupdates a time alignment, the UE initiates or restarts a time alignmenttimer. The UL grant includes an uplink resource allocation and atransmit power command (TPC) that are used to send a scheduling message(third message) to be described later. The TPC is used to determinetransmission power for a scheduled PUSCH.

After the UE transmits the random access preamble, the UE attempts toreceive its own random access response within a random access responsewindow that the eNB indicates through system information or a handovercommand, detects a PDCCH masked with an RA-RNTI corresponding to PRACH,and receives a PDSCH indicated by the detected PDCCH. Information aboutthe random access response may be transmitted in the form of a MACpacket data unit (PDU), and the MAC PDU may be transferred via thePDSCH.

If the UE successfully receives a random access response having the samerandom access preamble index/identifier as the random access preamblethat has been transmitted to the eNB, the UE stops the monitoring of therandom access response. On the other hand, if the UE does not receive arandom access response message until the random access response windowis terminated, or the UE does not receive a valid random access responsehaving the same random access preamble index as the random accesspreamble that has been transmitted to the eNB, the UE considers thereception of the random access response as a failure and then mayperform preamble retransmission.

(3) Third message (Msg 3, message 3)

If the UE receives a random access response valid for itself, the UEprocesses each of information included in the random access response.That is, the UE applies a TAC and stores a TC-RNTI. Further, the UEtransmits data stored in a buffer of the UE or newly generated data tothe eNB using the UL grant.

In case of a first connection of the UE, an RRC connection request thatis generated in the RRC layer and is transferred via a CCCH may beincluded in a third message and transmitted. In case of an RRCconnection re-establishment procedure, an RRC connectionre-establishment request that is generated in the RRC layer and istransferred via a CCCH may be included in the third message andtransmitted. Further, the third message may include an NAS accessrequest message.

The third message should include an identifier of the UE. There are twomethods for including the identifier of the UE in the third message. Ina first method, if the UE already had a valid cell identifier (C-RNTI)allocated in a corresponding cell prior to the random access procedure,the UE transmits its own cell identifier through an uplink transmissionsignal corresponding to the UL grant. On the other hand, if a valid cellidentifier was not allocated to the UE prior to a random accessprocedure, the UE transmits including its own unique identifier (e.g.,S-TMSI (SAE temporary mobile subscriber identity) or random number). Ingeneral, the unique identifier is longer than a C-RNTI.

If the UE transmitted data corresponding to the UL grant, it initiates acontention resolution timer.

(4) Fourth Message (Msg 4, Message 4)

If the eNB receives a C-RNTI of the corresponding UE from the UE throughthe third message, the eNB sends a fourth message to the UE using thereceived C-RNTI. On the other hand, if the eNB receives a uniqueidentifier (i.e., S-TMSI or random number) from the UE through the thirdmessage, the eNB sends the fourth message to the UE using a TC-RNTIallocated to the corresponding UE in a random access response. Forexample, the fourth message may include an RRC connection setup message.

The UE transmits data including its own identifier through the UL grantincluded in the random access response, and then waits for aninstruction of the eNB for a contention resolution. That is, the UEattempts to receive a PDCCH in order to receive a specific message.There are two methods for receiving the PDCCH. As described above, ifthe identifier of the UL in the third message transmitted in response tothe UL grant is C-RNTI, the UE attempts to receive the PDCCH using itsown C-RNTI, and if the identifier of the UL is a unique identifier(i.e., S-TMSI or random number), the UE attempts to receive the PDCCHusing a TC-RNTI included in the random access response. Afterwards, inthe former case, if the UE received the PDCCH through its own C-RNTIbefore the contention resolution timer expires, the UE determines thatthe random access procedure has been normally performed, and terminatesthe random access procedure. In the latter case, if the UE received thePDCCH through the TC-RNTI before the contention resolution timerexpires, the UE checks data to which a PDSCH indicated by the PDCCH istransferred. If the unique identifier of the UE was included in contentsof the data, the UE determines that the random access procedure has beennormally performed, and terminates the random access procedure. The UEobtains the C-RNTI through the fourth message. Afterwards, the UE and anetwork transmit and receive a UE-dedicated message using the C-RNTI.

Unlike the contention based random access procedure illustrated in FIG.5 , the operation in the non-contention based random access procedure isterminated by only the transmission of the first message and the secondmessage. That is, the UE is allocated a random access preamble from theeNB before transmitting to the eNB the random access preamble as thefirst message, transmits to the eNB the allocated random access preambleas the first message, and receives a random access response from theeNB, thereby terminating the random connection procedure.

RRC Connection Re-Establishment Procedure

An RRC connection re-establishment procedure is described in more detailbelow.

FIG. 6 illustrates an example of an RRC connection re-establishmentprocedure to which the present invention is applicable.

Referring to FIG. 6 , the UE stops using all radio bearers, that havebeen configured, except SRB 0 (signaling radio bearer #0), andinitializes various sub-layers of access stratum (AS) in S610.

The UE configures each sub-layer and a physical layer as a defaultconfiguration. During such a process, the UE maintains an RRC connectionstate.

The UE performs a cell selection procedure for performing an RRCconnection re-establishment procedure in S620. The cell selectionprocedure of the RRC connection re-establishment procedure may beperformed in the same manner as a cell selection procedure that the UEperforms in the idle state although the UE maintains the RRC connectionstate.

After the UE performs the cell selection procedure, the UE checks systeminformation of a corresponding cell and determines whether thecorresponding cell is an appropriate cell or not in S630. If theselected cell is determined as an appropriate E-UTRAN cell, the UE sendsan RRC connection re-establishment request message to the correspondingcell in S640.

If the selected cell through the cell selection procedure for performingthe RRC connection re-establishment procedure is determined as a cellusing other RAT other than E-UTRAN, the UE stops the RRC connectionre-establishment procedure and enters an RRC idle state in S650.

The UE may be configured so that the appropriateness check of the cellthrough the cell selection procedure and system information reception ofthe selected cell is completed within a limited time. To this end, theUE may run a timer as the UE initiates the RRC connectionre-establishment procedure. The timer may be stopped if it is determinedthat the UE selected the appropriate cell. If the timer expires, the UEconsiders the RRC connection re-establishment procedure as a failure andmay enter the RRC idle state. Hereinafter, the timer is referred to as aradio link failure timer. In LTE Spec TS 36.331, a timer called T311 maybe utilized as a radio link failure timer. The UE may obtain aconfiguration value of the timer from system information of a servingcell.

If the cell receives the RRC connection re-establishment request messagefrom the UE and accepts the request, the cell sends an RRC connectionre-establishment message to the UE.

The UE receiving the RRC connection re-establishment message from thecell reconfigures a PDCP sub-layer and a RLC sub-layer for SRB1.Further, the UE calculates again various key values related to securityconfiguration and reconfigures the PDCP sub-layer responsible forsecurity as the newly calculated security key values.

Hence, the SRB1 between the UE and the cell is open, and the UE and thecell can exchange RRC control messages. The UE completes the resume ofthe SRB1 and sends, to the cell, an RRC connection re-establishmentcomplete message that the RRC connection re-establishment procedure hasbeen completed in S660.

On the other hand, if the cell receives the RRC connectionre-establishment request message from the UE and does not accepts therequest, the cell sends an RRC connection re-establishment rejectmessage to the UE.

If the RRC connection re-establishment procedure is successfullyperformed, the cell and the UE perform the RRC connectionre-establishment procedure. Hence, the UE recovers the state prior tothe execution of the RRC connection re-establishment procedure, andmaximally guarantees continuity of service.

Sidelink Communication Monitoring

FIG. 7 illustrates an example of a procedure of transmitting andreceiving sidelink UE information (sidelinkUEInformation).

The purpose of this procedure is to inform the E-UTRAN that the UE ismore interested or no longer interested to receive sidelinkcommunication or discovery, not only request allocation or release oftransmission resources for sidelink communication or discoveryannouncement or V2X sidelink communication or sidelink discovery gap butalso receive the V2X sidelink communication, and report parametersrelated to sidelink discovery from system information ofinter-frequency/PLMN cell.

Next, sidelink communication monitoring is described.

A UE capable of sidelink communication that is configured by upperlayers to receive sidelink communication:

1> if the conditions for sidelink communication operation are met:

2> if in coverage on the frequency used for sidelink communication:

3> if a cell chosen for sidelink communication reception broadcastsSystemInformationBlockType18 including commRxPool:

4> configures lower layers to monitor sidelink control information andcorresponding data using the pool of resources indicated by commRxPool.

If commRxPool includes one or more entries including rxParametersNCell,the UE may monitor only such entries if associated primarysynchronization signal (PSS)/secondary synchronization signal (SSS) orsidelink synchronization signal (SLSS) ID is detected. When monitoringsuch pool, the UE applies timing of the concerned PSS/SSS or SLSS.

2> Else, if out of coverage of the sidelink carrier (i.e., frequencyused for sidelink communication):

3> the UE configures lower layers to monitor sidelink controlinformation and the corresponding data using the pool of resources thatwere preconfigured.

The UE may monitor if the UE does not have a selected SyncRef UE inaccordance with the timing of the selected SyncRef UE or based on theUE's own timing.

Sidelink Communication Transmission

A UE capable of sidelink communication that is configured by upperlayers to transmit non-relay related sidelink communication and hasrelated data to be transmitted, or a UE capable of relay relatedsidelink communication that is configured by upper layers to transmitrelay related sidelink communication and satisfies the conditions forrelay related sidelink communication:

1> if the conditions for sidelink communication operation are met:

2> if in coverage on the frequency used for sidelink communication:

3> if the UE is in an RRC_CONNECTED state and uses the PCell forsidelink communication:

4> if the UE is configured, by the current PCell/the PCell in which aphysical layer problem or a radio link failure was detected, withscheduled commTxResources:

5> if T310 or T311 is running; and if the PCell at which the UE detectedthe physical layer problem or the radio link failure broadcastsSystemInformationBlockType18 including commTxPoolExceptional; or

5> if T301 is running and the cell on which the UE initiated connectionre-establishment broadcasts SystemInformationBlockType18 includingcommTxPoolExceptional:

6> configures lower layers to transmit sidelink control information andcorresponding data using the pool of resources indicated by a firstentry in commTxPoolExceptional;

5> else:

6> configures lower layers to request E-UTRAN to assign transmissionresources for sidelink communication;

4> else if the UE is configured with commTxPoolNormalDedicated orcommTxPoolNormalDedicatedExt:

5> if priorityList is included for the entries ofcommTxPoolNormalDedicated or commTxPoolNormalDedicatedExt:

6> configures lower layers to transmit the sidelink control informationand the corresponding data using the one or more pools of resourcesindicated by commTxPoolNormalDedicated or commTxPoolNormalDedicatedExti.e. indicates all entries of this field to lower layers;

5> else:

6> configures lower layers to transmit the sidelink control informationand the corresponding data using the pool of resources indicated by thefirst entry in commTxPoolNormalDedicated;

3> else (i.e. sidelink communication in RRC_IDLE or on cell other thanPCell in RRC_CONNECTED):

4> if the cell chosen for sidelink communication transmission broadcastsSystemInformationBlockType18:

5> if SystemInformationBlockType18 includes commTxPoolNormalCommon:

6> if priorityList is included for the entries of commTxPoolNormalCommonor commTxPoolNormalCommonExt:

7> configures lower layers to transmit the sidelink control informationand the corresponding data using the one or more pools of resourcesindicated by commTxPoolNormalCommon and/or commTxPoolNormalCommonExt,i.e., indicates all entries of these fields to lower layers;

6> else:

7> configures lower layers to transmit the sidelink control informationand the corresponding data using the pool of resources indicated by thefirst entry in commTxPoolNormalCommon;

5> else if SystemInformationBlockType18 includes commTxPoolExceptional:

6> from the moment the UE initiates connection establishment untilreceiving an RRCConnectionReconfiguration including sl-CommConfig oruntil receiving an RRCConnectionRelease or an RRCConnectionReject;

7> configures lower layers to transmit the sidelink control informationand the corresponding data using the pool of resources indicated by thefirst entry in commTxPoolExceptional;

2> else (i.e. out of coverage on sidelink carrier):

3> if priorityList is included for the entries of preconfigComm inSL-Preconfiguration:

4> configures lower layers to transmit the sidelink control informationand the corresponding data using the one or more pools of resourcesindicated by preconfigComm, i.e., indicates all entries of this field tolower layers and in accordance with the timing of the selected SyncRefUE, or if the UE does not have a selected SyncRef UE, based on the UEsown timing;

3> else:

4> configures lower layers to transmit the sidelink control informationand the corresponding data using the pool of resources that werepreconfigured.

The conditions for relay related sidelink communication are as follows.

1> if the transmission concerns sidelink relay communication; and the UEis capable of sidelink relay or sidelink remote operation:

2> if the UE is in RRC_IDLE; and if the UE has a selected sidelink relayUE: the UE configures lower layers to transmit the sidelink controlinformation and the corresponding data using the specific resources,only if the following condition is met:

3> if the sidelink remote UE threshold conditions are met; and if the UEconfigured lower layers with a pool of resources included inSystemInformationBlockType18 (e.g., commTxPoolNormalCommon,commTxPoolNormalCommonExt or commTxPoolExceptional);commTxAllowRelayCommon is included in SystemInformationBlockType18;

2> if the UE is in RRC_CONNECTED: the UE configures lower layers totransmit the sidelink control information and the corresponding datausing the specific resources, only if the following condition is met:

3> if the UE configured lower layers with resources provided bydedicated signalling (i.e., commTxResources); the UE is configured withcommTxAllowRelayDedicated set to ‘true’.

The technology for a relay operation may be performed via various links(i.e. UE-to-UMTS (Uu) and PC5 (ProSe communication 5, proximitycommunication 5)).

That is, the relay operation may be applied to various networks (i.e.,narrow band-Internet of things (NB-IoT) or new radio access (NR)).

As illustrated in FIG. 8 to be described below, in NB-IoT network, aremote UE may be connected with a relay UE and may be connected with anetwork (or eNB).

Based on L2 relay, the eNB has to store both UE contexts (e.g., RRC) ofthe relay UE and the remote UE.

Hence, the remote UE may establish either direct connection (i.e., Uuinterface with the eNB) or indirect connection (i.e., PC5 interface withthe relay UE) and transmit data.

Since the remote UE can support both connections (Uu and PC5) and a path(or route) (re)selection between the connections is also supported, anappropriate path reselection is necessary if an abrupt radio linkfailure (RLF) is detected.

In case of each remote UE, there may be a trouble using the Uu link,especially, to enhance a coverage area due to a limited RF chaincapacity.

In the NR network, the path reselection problem mentioned above mayoccur as well.

Since NR network nodes (e.g., integrated access and backhaul (IAB) node)are connected with forming multiple hops, a suitable path should beselected. Detailed content related to this is described below.

Such a path (re)selection scheme is necessary to support servicecontinuity, and the RLF occurs among the NR nodes.

However, since a legacy path reselection procedure is considered only bypath reselection conditions based on a reference signal received power(RSRP), it does not deal with various unexpected RLF occurrences.

Moreover, in the legacy path reselection procedure, various datacharacteristics (e.g., 5QI (5G QoS Indicator), QCI (QoS ClassIdentifier) level, delay tolerant, beam state, etc.) of the remote UEand NR nodes are not considered to perform the path reselection.

Hereinafter, a method for reselecting, by a device or a node, a pathupon occurrence of the RLF proposed in the present specification isdivided and described into (1) NB-IoT network and (2) NR network.

First Embodiment

A first embodiment relates to a path reselection scheme in the NB-IoTnetwork.

In advance to describe the first embodiment, it is assumed that a remoteUE has an RRC connection with an eNB.

In the first embodiment, the remote UE and a relay UE may be expressedas an NB-IoT UE or an NB-IoT device, etc., and may be respectivelyreferred to as a first NB-IoT device and a second NB-IoT device.

Hereinafter, the remote UE and the relay UE are used for convenience ofexplanation.

Uu link conditions (link conditions between the remote UE and the eNB)may be seriously degraded due to a limited RF capacity of the remote UEin an enhanced coverage area.

Consequently, an abrupt radio link failure (RLF) may occur on a Uu link.

That is, the first embodiment represents a path reselection scheme bythe remote UE when the abrupt RLF occurs on the Uu link between theremote UE and the eNB.

In specific, if the remote UE detects an RLF on the Uu link (or Uuinterface), the remote UE initiates a (connection) re-establishmentprocedure in order to recover the RLF.

The remote UE considers whether the reestablishment procedure isperformed by a sidelink or not.

It may determine a recovery procedure based on various characteristicsof remote UE's data.

If a priority of data of the remote UE is low (e.g., delay tolerant),the recovery procedure is performed via the sidelink in order to reduceenergy consumption.

Otherwise, if a priority of data is high, the recovery procedure isperformed via an established Uu link.

In addition, the remote UE does not maintain a PC5 connection forreducing energy consumption, instead it can initiate to establish thePC5 connection only when it is necessary (i.e. upon the re-establishmentprocedure).

The first embodiment, i.e., the path reselection scheme in the NB-IoTnetwork may be performed by the following two methods (Method 1 andMethod 2).

Method 1: Path Reselection by Various Factors

Method 1 describes that a path reselection scheme by a remote UE isperformed by various factors such as QCI, delay, energy, etc.

The path reselection scheme by the Method 1 is performed by thefollowing steps, and each step is described in detail below.

First, the remote UE establishes an RRC connection with an eNB andreceives from the eNB transmission and/or reception resourceconfiguration via dedicated signaling with the eNB (Step 1).

In the present specification, ‘A and/or B’ can be interpreted in thesame sense as ‘including at least one of A or B’.

Next, the criteria of path reselection thresholds for various factors(either Uu or PC5) are configured from the eNB (Step 2).

Next, the remote UE initiates downlink/uplink transmission via Uuconnection (Step 3).

Next, an RLF occurs on a Uu link, and the RLF is detected by the remoteUE (Step 4).

Next, it is assumed that the remote UE initiates to establish PC5connection after data is determined to be transmitted over PC5 (Step 5).

Next, after the remote UE detects the RLF, the remote UE performs a pathreselection that initiates a re-establishment procedure in order torecover the RLF (Step 6).

Next, the remote UE considers the followings in order to reselect a path(Step 7).

That is, the remote UE determines whether to perform an RLF recoveryprocess via the sidelink or the Uu link according to the followingconditions.

Specifically, the remote UE selects the sidelink in order to perform theRLF recovery process in the following cases (Step 7-1).

If a lowest QCI level of established bearers is higher than a thresholdQCI,

If a delay budget (e.g. packet delay budget (PDB)) is higher than athreshold delay,

If a highest bearer priority or a logical channel priority of theestablished bearers is lower than a threshold priority,

If a highest ProSe-per-packet priority (PPPP) of the established bearersis higher than a PPPP threshold,

-   -   If a remaining battery of the remote UE is lower than a        threshold,

The remote UE selects the Uu link in order to perform the RLF recoveryprocess in the following cases (Step 7-2).

If a lowest QCI level of the established bearers is lower than or equalto the threshold QCI,

If a delay budget (e.g. packet delay budget (PDB)) is lower than orequal to the threshold delay,

If a highest bearer priority or a logical channel priority of theestablished bearers is higher than or equal to the threshold priority,

If a highest PPPP of the established bearers is lower than or equal tothe PPPP threshold,

-   -   If a remaining battery of the remote UE is higher than or equal        to the threshold,

If the remote UE satisfies the conditions mentioned in the step 7-2 andselects the Uu link, the existing RRC connection re-establishmentprocedure is performed.

Alternatively, if the remote UE satisfies the conditions mentioned inthe step 7-1 and selects the sidelink, the remote UE sends are-establishment request message to a network via a relay UE.

Then, the network sends a response message to the remote UE via therelay UE.

If the RLF is recovered in the step 7-1, the following step 8 isperformed. If the RLF is recovered in the step 7-2, the following step10 is performed.

In the above, the threshold may be provided via broadcast signaling ordedicated signaling or preconfigured.

The step 8 is as follows.

If the relay UE is not detected in proximity, the remote UE cannotperform a path reselection. Hence, the remote UE selects the Uu link.

Alternatively, if there is no linked relay UE supporting the servicewhich the remote UE has used, the remote UE selects the Uu link. Then,the step 10 is performed.

If the relay UE is detected in proximity, the remote UE can determine toperform a path reselection via the sidelink.

Hence, the remote UE establishes PC5 connection with the detected relayUE. Then, step 9 is performed.

Next, the remote UE can transmit/receive data that can be relayed by therelay UE (e.g., in case of PC5) (Step 9).

Next, the remote UE performs a re-establishment procedure with thenetwork (Step 10).

Then, the remote UE can transmit/receive data to/from the eNB.

Method 2: Path reselection by reference signal received power (RSRP)

Method 2 relates to a path reselection scheme performed by RSRP, andspecifically, is performed by the following steps.

First, a remote UE establishes an RRC connection with an eNB andreceives from the eNB transmission and/or reception resourceconfiguration via dedicated signaling with the eNB (Step 1).

Next, the criteria of path reselection thresholds (either Uu or PC5) areconfigured from the eNB (Step 2).

Next, the remote UE initiates downlink/uplink transmission with the eNBvia Uu connection (Step 3).

Next, an RLF occurs on a Uu link, and the RLF is detected by the remoteUE (Step 4).

Next, if data is determined to be transmitted over PC5, it is assumedthat the remote UE initiates to establish PC5 connection (Step 5).

Next, after the remote UE detects the RLF, the remote UE performs a pathreselection that initiates a re-establishment procedure in order torecover the RLF (Step 6).

Next, in advance to perform the path reselection by the remote UE, theremote UE compares received RSRP with sidelink (SD)-RSRP (Step 7).

The Step 7 may be further specified by the following steps 7-1 to 7-4.

That is, if measured SD-RSRP is higher than a RSRP threshold, the remoteUE selects a sidelink path. Otherwise, the remote UE selects the Uu link(Step 7-1).

If measured RSRP of a selected cell is higher than the RSRP threshold,the remote UE selects the Uu link. Otherwise, the remote UE selects thesidelink (Step 7-2).

If measured RSRP of the selected cell is lower than a threshold, andsidelink quality (e.g. SD-RSRP) between the remote UE and a relay UE ishigher than another threshold, the UE selects the sidelink. Otherwise,the remote UE selects the Uu link (Step 7-3).

If measured RSRP of the selected cell is lower than measured sidelinkquality between the remote UE and the relay UE, the UE selects thesidelink. Otherwise, the remote UE selects the Uu link (Step 7-4).

If the remote UE selects the Uu link, the existing RRC connectionre-establishment procedure is performed.

If the remote UE selects the sidelink, the remote UE sends are-establishment request message to a network via the relay UE.

Then, the network sends a response message to the remote UE via therelay UE.

Next, step 8 is described.

If the relay UE is not detected in proximity, the remote UE cannotperform a path reselection. Hence, the remote UE selects the Uu link.

Alternatively, if there is no linked relay UE supporting the servicewhich the remote UE has used, the remote UE selects the Uu link. Then,the following step 10 is performed.

Alternatively, if the relay UE is detected in proximity, the remote UEcan determine to perform a path reselection via the sidelink. Hence, theremote UE establishes PC5 connection with the detected relay UE. Then,the following step 9 is performed.

Next, the step 9 is described.

The remote UE transmits/receives data that can be relayed by the relayUE (e.g., in case of PC5) (Step 9).

Next, the step 10 is described.

Next, the remote UE performs a re-establishment procedure with thenetwork. Then, the remote UE transmits/receives data to/from the eNB.

FIG. 8 illustrates an example of a path reselection procedure when a RLFoccurs in a NB-IoT network proposed by the present specification.

First, if a RLF occurs on a Uu link between an eNB and a remote UE(S810), the remote UE determines a path (or route) for recovering theRLF (S820).

In the same manner, the remote UE and a relay UE may be expressed as anNB-IoT UE or an NB-IoT device, etc.

First, in the step S820, if the remote UE determines a Uu link as an RLFrecovery path, the remote UE performs an RRC connection re-establishmentprocedure with the eNB (S830).

Alternatively, in the step S820, if the remote UE determines a sidelink(or PC5) as the RLF recovery path, the remote UE performs are-establishment procedure with the eNB (or network) via a relay UE(S840).

Specifically, the remote UE sends a re-establishment request message tothe eNB (or network) via the relay UE.

Then, the eNB sends a response message to the remote UE via the relay UEand thus performs an RLF recovery procedure.

FIG. 9 is a flow chart illustrating an example of a path reselectionscheme by a UE proposed by the present specification.

More specifically, FIG. 9 illustrates a method for performing, by afirst user equipment (UE), a RLF recovery procedure in a wirelesscommunication system.

It is assumed that the first UE is connected to a base station via aUE-to-UMTS (Uu) link and is connected to a second UE via a sidelink.

For example, the first UE may be a remote UE, and the second UE may be arelay UE.

First, if a RLF is detected on the Uu link, the first UE determines apath for performing the RLF recovery procedure (S910).

The path for performing the RLF recovery procedure may be determinedbased on a factor related to data characteristic of the first UE.

For example, the factor related to the data characteristic of the firstUE may be a Qos class identifier (QCI), a packet delay budget, apriority, and the like.

Next, the first UE performs an RRC connection re-establishment procedurein order to recover the RLF through the determined path (S920).

The determined path may be the Uu link or the sidelink.

Referring more specifically to the determination of the path, the firstUE receives, from the base station, a threshold for the factor relatedto the data characteristic of the first UE.

The first UE compares the factor related to the data characteristic ofthe first UE with the received threshold and thus can determine the pathfor performing the RLF recovery procedure.

If the determined path is the sidelink, the first UE sends, to thesecond UE, a request message for requesting a RRC connectionre-establishment and receives, from the second UE, a response message tothe request message, in order to perform the RRC connectionre-establishment procedure.

Integrated Access Backhaul (IAB)

IAB corresponds to technology that can be used for 5G or NR in that itenables flexible and very dense deployment of new radio access (NR)cells without the need for densifying a transport network.

In regard to the IAB in NR, a topology management for single hop andmulti-hop connections has been discussed.

Multi-hop backhauling provides wider coverage extension than single hop.

Further, the multi-hop backhauling can enable backhauling aroundobstacles.

The number of hops may be variously configured depending on variousfactors (e.g., deployment scenario, traffic load, frequency, etc.).

In such a topology structure, multiple relay nodes (e.g., anchor nodes,relay nodes) are connected between an NR core network and a UE.

Hierarchically, the NR core network may be connected to an anchor node(e.g., donor node), and many relay nodes may be connected to the anchornode.

FIG. 10 illustrates an example of an IAB topology structure.

More specifically, FIG. 10 a illustrates a single-hop backhaulstructure, and FIG. 10 b illustrates a multi-hop backhaul structure.

In FIG. 10 , a donor node corresponding to an anchor node may beconnected to an NG core, one or more IAB nodes (or relay nodes) may beconnected to the donor node, and one or more devices may be connected tothe IAB nodes.

FIG. 11 illustrates an example of in-band and out-band IABs.

In-band IAB represents that an access link and a backhaul link at leastpartially overlap on frequency, and out-band IAB represents that anaccess link and a backhaul link can operate independently.

In-band IAB scenarios including the access and backhaul links(TDM/FDM/SDM) subject to half-duplex constraint at an IAB node can besupported.

Out-band IAB scenarios can also be supported using the same set of RANfunctions designed for in-band scenarios.

In the NR, it may be critical to study in-band operation which requiresinterworking with the access link to accommodate the half-duplexconstraints (e.g., when the IAB node cannot transmit and receivesimultaneously on the carrier) and avoid (or mitigate) interference.

Further, IAB can operate in both mmWave and sub-6 GHz (or below 6 GHz).

Second Embodiment

A second embodiment relates to a path reselection scheme in a NRnetwork.

Based on the above description, a method for performing a pathre-establishment procedure of a remote UE proposed by the presentspecification in the NR network is described below.

Here, ‘path re-establishment’ or ‘path reselection’ used in the presentspecification can be interpreted in the same sense.

In the NR network, the path reselection problem mentioned above mayoccur as well.

FIG. 12 illustrates an example of a situation where a path reselectionis necessary in an NR network.

With reference to FIG. 12 , it illustrates a situation where a pathbetween IAB donor 1 and IAB node cannot be used as a RLF, etc. In thiscase, data can be exchanged between IAB donor 2 and the IAB node througha path reselection.

Since NR network nodes (e.g., IAB relay nodes) are connected withforming multiple hops, a suitable path should be selected.

Such a path reselection scheme is necessary to support servicecontinuity while the RLF occurs.

Therefore, it is necessary how to determine and reselect the suitablepath based on various factors.

The present specification considers a 5G QoS indicator (5QI) which isapplied to a QoS parameter since it reflects and map detailedcharacteristic of a specific data flow.

In addition, a specific congestion level of the hop is different sinceeach node works as a UE and backhaul, respectively.

The path reselection may be performed by a distributed manner or acentralized manner.

When the distributed manner is applied, assistance information will benecessary among relay nodes.

The assistance information may be transmitted, for example, periodicallyor based on event triggered.

A method for performing, by a specific node (e.g., relay node), a pathselection in the NR network is described in detail below.

Here, the specific node may be expressed as a gNB, a base station, anetwork, a device, etc.

Hereinafter, the specific node is expressed as a relay node forconvenience of explanation.

The second embodiment is performed by various factors such as 5QI,slice/service type (enhanced mobile broadband (eMBB), ultra reliable lowlatency communication (URLLC), MIoT), a congestion (load) level, a beamstate, etc.

In this case, the beam state may correspond to whether beam directionsmatch between relay nodes, beam on or off of the relay node, beammanagement of the relay node, or the like.

In addition, the beam direction coincidence may use a quasi co-location(QCL) with a channel state information-reference signal (CSI-RS), asounding reference signal (SRS), a synchronization signal block (SSB),and the like.

The second embodiment is performed by the following steps, withreference to FIG. 13 . That is, FIG. 13 is a diagram illustrating anexample of an NR network proposed in the present specification.

First, the donor gNB is connected to a 5G (or NR) core network, and anumber of relay nodes (eg, IAB nodes) are connected to the donor nodethrough Uu.

It is assumed that the PC5 link is not connected between multiple relaynodes.

And, the path reselection threshold for various factors (Uu or PC5) isset at the eNB.

The relay node initiates downlink and/or uplink transmission with thedonor gNB via the Uu connection (step 1).

Next, the relay node exchanges assistance information for pathreselection with the donor gNB (step 2).

The assistance information may be exchanged periodically or in an eventtriggered manner.

Next, the RLF occurs on one of the Uu links, and the RLF is detected bya proximity relay node (step 3).

Next, when the RLF is detected, the relay node performs path reselectionto initiate reestablishment to recover the RLF (step 4).

If no RLF is detected, an appropriate path may be selected under certainconditions. In other words, let's look at five steps.

If the following conditions are met, the relay node reselects the relaynode's relaying path with relay node reselection.

If the 5QI level of bearers established and the data flows associatedwith it are supported by the node

-   -   If the relay node supports the relevant slice type or specific        service    -   If relay node supports slice/service type such as eMBB    -   If relay node supports slice/service type such as URLLC    -   If the relay node supports a slice/service type such as MIoT (or        mMTC (massive machine type communication))    -   If a relay node supports a particular service associated with it    -   If the allowable delay budget (e.g. PDB (Packet Delay Budget))        is higher than the threshold delay or higher than other        neighboring nodes

Congestion level is lower than the threshold or lower than otherneighboring nodes

If any one of the above conditions is met, the relay node performs apath reselection procedure with the selected relay node (step 6).

Here, the path reselection may be performed in a distributed manner or acentralized manner.

FIG. 14 is a flowchart illustrating still another example of a methodfor reselecting a path by a terminal proposed in the presentspecification.

That is, FIG. 14 illustrates a method of reselecting a relaying path bya first node in a wireless communication system.

It is assumed that the first node is connected to the second nodethrough a Uu (UE-to-UMTS) link, and the other node and the PC5 link (orsidelink) are not connected.

For example, the first node may be a relay node and the second node maybe a donor node.

In addition, the second node may be connected to a 5G core network.

First, a first node transmits and receives data with at least one nodethrough the Uu link (S1410).

Here, at least one node may mean another relay node.

Next, when a radio link failure (RLF) is detected in the Uu link or aspecific condition is satisfied, the first node reselects a relayingpath (S1420).

The reselection of the relaying path according to the specific conditionmay be a case where no RLF is detected in the Uu link.

Here, the specific condition may be whether to support a 5QI level on anode, whether to support a specific service type on the node, or acongestion level of a hop.

For example, the specific service type may be enhanced multimediabroadband (eMBB), ultra reliable low latency communication (URLLC), ormassive IoT (MIoT).

Next, the first node transmits and receives data with the at least onenode through the reselected relaying path (S1430).

If the relaying path is reselected using a distributed manner, the firstnode may exchange assistance information with the at least one node.

In this case, the assistance information may be exchanged periodicallyor in an event triggered manner.

Overview of Device to which the Present Invention is Applicable

FIG. 15 illustrates a block configuration diagram of a wirelesscommunication device according to an embodiment of the presentinvention.

Referring to FIG. 15 , a wireless communication system includes a basestation (or network) 1510 and a UE 1520.

The base station 1510 includes a processor 1511, a memory 1512, and acommunication module 1513.

The processor 1511 implements functions, processes, and/or methodsproposed in FIGS. 1 to 14 . Layers of wired/radio interface protocol maybe implemented by the processor 1511. The memory 1512 is connected tothe processor 1511 and stores various types of information for drivingthe processor 1511. The communication module 1513 is connected to theprocessor 1511 and transmits and/or receives wired/radio signals.

The communication module 1513 may include a radio frequency (RF) unit(or RF module) for transmitting/receiving a radio signal.

The UE 1520 includes a processor 1521, a memory 1522, and acommunication module (or RF unit) 1523. The processor 1521 implementsfunctions, processes, and/or methods proposed in FIGS. 1 to 14 . Layersof radio interface protocol may be implemented by the processor 1521.The memory 1522 is connected to the processor 1521 and stores varioustypes of information for driving the processor 1521. The communicationmodule 1523 is connected to the processor 1521 and transmits and/orreceives a radio signal.

The memories 1512 and 1522 may be inside or outside the processors 1511and 1521 and may be connected to the processors 1511 and 1521 throughvarious well-known means.

Further, the base station 1510 and/or the UE 1520 may have a singleantenna or multiple antennas.

FIG. 16 illustrates a block configuration diagram of a communicationdevice according to an embodiment of the present invention.

In particular, FIG. 16 illustrates in more detail the UE illustrated inFIG. 15 .

Referring to FIG. 16 , the UE may include a processor (or digital signalprocessor (DSP)) 1610, an RF module (or RF unit) 1635, a powermanagement module 1605, an antenna 1640, a battery 1655, a display 1615,a keypad 1620, a memory 1630, a subscriber identification module (SIM)card 1625 (which is optional), a speaker 1645, and a microphone 1650.The UE may also include a single antenna or multiple antennas.

The processor 1610 implements functions, processes, and/or methodsproposed in FIGS. 1 to 14 . Layers of a radio interface protocol may beimplemented by the processor 1610.

The memory 1630 is connected to the processor 1610 and storesinformation related to operations of the processor 1610. The memory 1630may be inside or outside the processor 1610 and may be connected to theprocessors 1610 through various well-known means.

A user inputs instructional information, such as a telephone number, forexample, by pushing (or touching) buttons of the keypad 1620 or by voiceactivation using the microphone 1650. The processor 1610 receives andprocesses the instructional information to perform an appropriatefunction, such as to dial the telephone number. Operational data may beextracted from the SIM card 1625 or the memory 1630. Further, theprocessor 1610 may display instructional information or operationalinformation on the display 1615 for the user's reference andconvenience.

The RF module 1635 is connected to the processor 1610 and transmitsand/or receives a RF signal. The processor 1610 forwards instructionalinformation to the RF module 1635 in order to initiate communication,for example, transmit a radio signal configuring voice communicationdata. The RF module 1635 consists of a receiver and a transmitter toreceive and transmit the radio signal. The antenna 1640 functions totransmit and receive the radio signal. Upon reception of the radiosignal, the RF module 1635 may forward a signal to be processed by theprocessor 1610 and convert the signal into a baseband. The processedsignal may be converted into audible or readable information output viathe speaker 1645.

FIG. 17 illustrates an example of a RF module of a wirelesscommunication device to which a method proposed by the presentspecification is applicable.

More specifically, FIG. 17 illustrates an example of an RF module thatcan be implemented in a frequency division duplex (FDD) system.

First, in a transmission path, the processor illustrated in FIGS. 15 and16 processes data to be transmitted and provides an analog output signalto a transmitter 1710.

In the transmitter 1710, the analog output signal is filtered by a lowpass filter (LPF) 1711 to remove images caused by a digital-to-analogconversion (ADC), is up-converted from a baseband to an RF by anup-converter (mixer) 1712, and is amplified by a variable gain amplifier(VGA) 1713, and the amplified signal is filtered by a filter 1714, isadditionally amplified by a power amplifier (PA) 1715, is routed throughduplexer(s) 1750/antenna switch(es) 1760, and is transmitted through anantenna 1770.

Further, in a reception path, the antenna 1770 receives signals from theoutside and provides the received signals, and the signals are routedthrough the antenna switch(es) 1760/duplexers 1750 and are provided to areceiver 1720.

In the receiver 1720, the received signals are amplified by a low noiseamplifier (LNA) 1723, are filtered by a bans pass filter 1724, and aredown-converted from the RF to the baseband by a down-converter (mixer)1725.

The down-converted signal is filtered by a low pass filter (LPF) 1726and is amplified by a VGA 1727 to obtain an analog input signal, and theanalog input signal is provided to the processor illustrated in FIGS. 15and 16 .

Further, a local oscillator (LO) generator 1740 generates transmittedand received LO signals and provides them to the up-converter 1712 andthe down-converter 1725, respectively.

In addition, a phase locked loop (PLL) 1730 receives control informationfrom the processor in order to generate the transmitted and received LOsignals at appropriate frequencies and provides control signals to theLO generator 1740.

The circuits illustrated in FIG. 17 may be arranged differently from theconfiguration illustrated in FIG. 17 .

FIG. 18 illustrates another example of a RF module of a wirelesscommunication device to which a method proposed by the presentspecification is applicable.

More specifically, FIG. 18 illustrates an example of an RF module thatcan be implemented in a time division duplex (TDD) system.

A transmitter 1810 and a receiver 1820 of the RF module in the TDDsystem have the same structure as the transmitter and the receiver ofthe RF module in the FDD system.

Hereinafter, only the structure of the RF module of the TDD system thatdiffers from the RF module of the FDD system will be described, and thesame structure will refers to the description of FIG. 17 .

A signal amplified by a power amplifier (PA) 1815 of the transmitter1810 is routed through a band select switch 1850, a band pass filter(BPF) 1860, and antenna switch(es) 1870 and is transmitted via anantenna 1880.

Further, in a reception path, the antenna 1880 receives signals from theoutside and provides the received signals, and the signals are routedthrough the antenna switch(es) 1870, the band pass filter 1860, and theband select switch 1850 and are provided to the receiver 1820.

The embodiments described above are implemented by combinations ofcomponents and features of the present invention in predetermined forms.Each component or feature should be considered selectively unlessspecified separately. Each component or feature may be carried outwithout being combined with another component or feature. Moreover, somecomponents and/or features are combined with each other and canimplement embodiments of the present invention. The order of operationsdescribed in embodiments of the present invention may be changed. Somecomponents or features of one embodiment may be included in anotherembodiment, or may be replaced by corresponding components or featuresof another embodiment. It is apparent that some claims referring tospecific claims may be combined with another claims referring to theclaims other than the specific claims to constitute the embodiment oradd new claims by means of amendment after the application is filed.

Embodiments of the present invention can be implemented by variousmeans, for example, hardware, firmware, software, or combinationsthereof. When embodiments are implemented by hardware, one embodiment ofthe present invention can be implemented by one or more applicationspecific integrated circuits (ASICs), digital signal processors (DSPs),digital signal processing devices (DSPDs), programmable logic devices(PLDs), field programmable gate arrays (FPGAs), processors, controllers,microcontrollers, microprocessors, and the like.

When embodiments are implemented by firmware or software, one embodimentof the present invention can be implemented by modules, procedures,functions, etc. performing functions or operations described above.Software code can be stored in a memory and can be driven by aprocessor. The memory is provided inside or outside the processor andcan exchange data with the processor by various well-known means.

It is apparent to those skilled in the art that the present inventioncan be embodied in other specific forms without departing from essentialfeatures of the present invention. Accordingly, the aforementioneddetailed description should not be construed as limiting in all aspectsand should be considered as illustrative. The scope of the presentinvention should be determined by rational construing of the appendedclaims, and all modifications within an equivalent scope of the presentinvention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

Although a method for performing a path reselection in a wirelesscommunication system according to the present invention has beendescribed focusing on examples applying to the 3GPP LTE/LTE-A system andthe 5G system, it can be applied to various wireless communicationsystems other than the systems.

The invention claimed is:
 1. A method for performing, by a first userequipment (UE), a radio link failure (RLF) recovery procedure in awireless communication system, the method comprising: determining a linkfor performing the RLF recovery procedure among (i) a UE-to-UMTS (Uu)link between the first UE and a base station and (ii) a sidelink betweenthe first UE and a second UE, based on a RLF of the Uu link beingdetected; and performing an RRC connection re-establishment procedurefor recovering the RLF of the Uu link based on the determined link,wherein based on that among the Uu link and the sidelink, only the Uulink is available for the RRC connection re-establishment procedure, theRRC connection re-establishment procedure is performed based on the Uulink, wherein based on that among the Uu link and the sidelink, only thesidelink is available for the RRC connection re-establishment procedure,the RRC connection re-establishment procedure is performed based on thesidelink, and wherein based on that among the Uu link and the sidelink,both the Uu link and the sidelink are available for the RRC connectionre-establishment procedure, the RRC connection re-establishmentprocedure is performed based on any one of the Uu link and the sidelink.2. The method of claim 1, further comprising: based on the RRCconnection re-establishment procedure being performed based on thesidelink: receiving, from the second UE, a message for performing theRRC connection re-establishment procedure.
 3. The method of claim 1,further comprising: receiving, from the base station, a threshold for afactor related to a data characteristic of the first UE.
 4. The methodof claim 3, wherein the link for performing the RLF recovery procedureis determined through a comparison between the factor related to thedata characteristic of the first UE and the received threshold.
 5. Themethod of claim 4, wherein the factor related to the data characteristicof the first UE is a Quality of Service (QoS) class identifier (QCI), apacket delay budget, or a priority.
 6. The method of claim 1, whereinthe first UE is a remote UE, and the second UE is a relay UE.
 7. A firstuser equipment (UE) for performing a radio link failure (RLF) recoveryprocedure in a wireless communication system, the first UE comprising: aradio frequency (RF) module configured to transmit and receive a radiosignal; a processor functionally connected to the RF module; and amemory functionally connected to the processor and storing instructionsthat, when executed by the processor, perform operations comprising:determining a link for performing the RLF recovery procedure among (i) aUE-to-UMTS (Uu) link between the first UE and a base station and (ii) asidelink between the first UE and a second UE, based on a RLF of the Uulink being detected; and performing an RRC connection re-establishmentprocedure for recovering the RLF of the Uu link based on the determinedlink, wherein based on that among the Uu link and the sidelink, only theUu link is available for the RRC connection re-establishment procedure,the RRC connection re-establishment procedure is performed based on theUu link, wherein based on that among the Uu link and the sidelink, onlythe sidelink is available for the RRC connection re-establishmentprocedure, the RRC connection re-establishment procedure is performedbased on the sidelink, and wherein based on that among the Uu link andthe sidelink, both the Uu link and the sidelink are available for theRRC connection re-establishment procedure, the RRC connectionre-establishment procedure is performed based on any one of the Uu linkand the sidelink.
 8. The first UE of claim 7, wherein the operationsfurther comprise: based on the RRC connection re-establishment procedurebeing performed based on the sidelink: receiving, from the second UE, amessage for performing the RRC connection re-establishment procedure. 9.The first UE of claim 7, wherein the operations further comprise:receiving, from the base station, a threshold for a factor related to adata characteristic of the first UE.
 10. The first UE of claim 9,wherein the link for performing the RLF recovery procedure is determinedthrough a comparison between the factor related to the datacharacteristic of the first UE and the received threshold.
 11. The firstUE of claim 10, wherein the factor related to the data characteristic ofthe first UE is a Quality of Service (QoS) class identifier (QCI), apacket delay budget, or a priority.
 12. The first UE of claim 7, whereinthe first UE is a remote UE, and the second UE is a relay UE.
 13. Aprocessing apparatus configured to control a first user equipment (UE)for performing a radio link failure (RLF) recovery procedure in awireless communication system, processing apparatus comprising: aprocessor; and a memory functionally connected to the processor andstoring instructions that, when executed by the processor, performoperations comprising: determining a link for performing the RLFrecovery procedure among (i) a UE-to-UMTS (Uu) link between the first UEand a base station and (ii) a sidelink between the first UE and a secondUE, based on a RLF of the Uu link being detected; and performing an RRCconnection re-establishment procedure for recovering the RLF of the Uulink based on the determined link, wherein based on that among the Uulink and the sidelink, only the Uu link is available for the RRCconnection re-establishment procedure, the RRC connectionre-establishment procedure is performed based on the Uu link, whereinbased on that among the Uu link and the sidelink, only the sidelink isavailable for the RRC connection re-establishment procedure, the RRCconnection re-establishment procedure is performed based on thesidelink, and wherein based on that among the Uu link and the sidelink,both the Uu link and the sidelink are available for the RRC connectionre-establishment procedure, the RRC connection re-establishmentprocedure is performed based on any one of the Uu link and the sidelink.